1. Field of the Invention
The invention relates to amine extractive separation methods and more particularly relates to methods for the separation of primary amines from tertiary amines which have close boiling points, by means of azeotropic distillation.
2. Description of Other Relevant Methods in the Field
Bis-(2-aminoethyl)ether (BAEE) and N-(2-methoxyethyl)morpholine (MEM) are co-products in the production of morpholine when diethylene glycol and ammonia are used as the reactor feed. These two co-products are very difficult to separate by conventional distillation because of their close boiling points. It would be advantageous to separate these two compounds because BAEE can be methylated to form .beta.-(N,N-dimethylaminoethyl)ether which is useful as catalyst in polyurethane isocyanate reactions according to U.S. Pat. No. 3,330,782, incorporated by reference herein.
No good method has been found for the separation of these two compounds. However, amines have been separated from other compounds according to some of the following techniques.
For example, U.S. Pat. No. 3,033,864 discloses the purification of pyrazines and piperazines by azeotropic distillation. In that patent, the goal was to remove unreacted alkanolamines by using co-distillation agents comprising aliphatic hydrocarbons, aromatic hydrocarbons and nuclear chlorinated aromatic hydrocarbons having normal boiling points between about 130.degree. C. and 200.degree. C. Representative examples given were octane and higher aliphatic hydrocarbons, petroleum fraction mixtures, ethyl cyclohexane, ethylbenzene, the xylenes, diethylbenzene, ethyl toluene, cumene and chlorobenzene.
A process for recovering piperazine from a mixture with triethylenediamine is described in U.S. Pat. No. 3,105,019. The inventors therein found that aliphatic hydrocarbons and especially saturated aliphatic hydrocarbons would be suitable azeotropic agents for the piperazine-triethylenediamine split if the boiling points were in the range from 110.degree. C. to about 200.degree. C., with particularly good results being obtained if the boiling point is within the range from about 140.degree. C. to about 160.degree. C. Specific compounds mentioned and tried were 3-methylheptane, 2-ethyl hexene, 1,2-dimethyl cyclohexane, meta-xylene, nonane, styrene, mesitylene, kerosene and 1-methyl naphthalene.
A method of recovering the major by-products from piperazine reaction residue is presented in U.S. Pat. No. 3,331,756. It was taught therein that hydrocarbons immiscible with diethylenetriamine and boiling within the range of about 175.degree. C. to about 250.degree. C. would be suitable entrainers for use in the separation of diethylenetriamine and aminoethylpiperazine. Two azeotropic agents mentioned were tetrapropylene and n-dodecane, with tetrapropylene being preferred because it gave a cleaner separation.
U.S.S.R. Pat. No. 472,122 teaches that diethylenetriamine and aminoethylpiperazine may be separated from reaction mixtures (especially those from the synthesis of a diamine and piperazine) by means of azeotropic rectification using a hydrocarbon mixture boiling at 160.degree. C. to 174.degree. C. yielding an azeotrope with DETA. The inventors found that the fractionation is simpler with n-decane than with dodecane or tetrapropylene.
The separation of an alkylene open chain polyamine from a piperazine compound may be accomplished by complexing the polyamine with a salt selected from the group consisting of sulfates and chlorides of copper, nickel, cobalt and zinc, according to the invention disclosed in U.S. Pat. No. 3,038,904. The complex compounds are extracted with substances such as chloroform or are allowed to precipitate out. U.S. Pat. No. 3,400,129 reveals that 2-methyl triethylenediamine can be purified in a process which incorporates a two-solvent extraction step. One of the solvents is water and the other is an organic solvent for pyrazines, such as hexene, octene, nonene, benzene, toluene, xylenes, ethyl benzene, propyl benzene, n-hexane, n-heptane, isooctane, n-nonane, methylnonane, chlorobenzene, chlorotoluenes, diethylether, furan and alkylbenzonitriles. The method includes an azeotropic distillation step where 2-methylpiperazine is distilled and a step where the purified 2-methyl triethylenediamine is recovered.
Other, less desirable methods for separating amines have been devised. For example, U.S. Pat. No. 3,420,828 to Muhlbauer uses ethylene oxide to react with BAEE to permit MEM to be distilled. U.S. Pat. No. 3,417,141 to Feldman, et al. teaches the separation of monoamines from diamines having six or more carbon atoms via liquid-liquid extraction with a polar solvent and a non-polar solvent. U.S. Pat. No. 3,038,904 to Godfrey reveals the separation of polyamines from piperazine compounds via application of metal sulfates or metal chlorides.
Further, U.S. Pat. No. 2,691,624 to Challis discloses a process for separating di-n-propylamine and tri-n-propylamine from a mixture containing di-n-propylamine, tri-n-propylamine, n-propanol and water by co-distilling with cyclohexane or benzene. The secondary amine content of an impure tertiary amine may be reduced by forming two organic phases based on the tertiary amine using hydrogen fluoride according to British Pat. No. 1,020,513 to Stevens, et al. Additionally, U.S.S.R. Pat. No. 472,122, as abstracted by Derwent, teaches the separation of diethylenetriamine and aminoethylpiperazine by azeotropic fractionation with hydrocarbons boiling at 160.degree.-174.degree. C. The separation of water soluble amines, such as morpholine, from their aqueous solutions may be accomplished by inert organic solvents miscible with the morpholine but not the water as taught by French Pat. No. 1,407,305. Further, Japanese Patent Document No. 55-127349 suggests simultaneous removal of water and picoline from primary arylamines by subjecting the mixture to distillation in the presence of toluene, according to the Derwent abstract.
Further, in Advances in Chemistry No. 116: Azeotropic Data III, 1973, L. H. Horsley lists a number of binary azeotropic systems.
Non-polar hydrocarbons such as methane, butane, isopentane, etc. are used in the separation of primary amines and tertiary amines according to U.S. patent application Ser. No. 581,465. These same non-polar hydrocarbons together with water are used in the extraction of the same close boiling amines, primary and tertiary, disclosed in U.S. patent application Ser. No. 581,464. Both of these applications were filed on Feb. 17, 1984.